1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that has two coils.
2. Description of the Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of a recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of a recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density when compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure in which a read head unit having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit having an induction-type electromagnetic transducer for writing are stacked on the top surface of a substrate. The write head unit includes a coil and a main pole. The coil produces a magnetic field corresponding to data to be written on a recording medium. The main pole allows a magnetic flux corresponding to the magnetic field produced by the coil to pass, and produces a write magnetic field in the direction perpendicular to the plane of the recording medium. The main pole has an end face located in a medium facing surface facing the recording medium.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically in the form of a slider. The slider has the medium facing surface. The medium facing surface has the air inflow end (the leading end) and the air outflow end (the trailing end). The slider is configured to slightly fly over the surface of the recording medium by means of an airflow that comes from the leading end into the space between the medium facing surface and the recording medium.
Here, the side of the positions closer to the leading end relative to a reference position will be defined as the leading side, and the side of the positions closer to the trailing end relative to the reference position will be defined as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
The magnetic head is typically disposed near the trailing end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In particular, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew can cause the phenomenon that signals already written on one or more tracks in the neighborhood of a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing. In the present application, this phenomenon will be called unwanted erasure. Unwanted erasure includes adjacent track erasure (ATE) and wide-area track erasure (WATE). To achieve higher recording density, it is necessary to prevent unwanted erasure.
As a technique for preventing unwanted erasure induced by the skew, U.S. Pat. No. 6,954,340 B2 and U.S. Patent Application Publication No. 2005/0128637 A1, for example, each disclose a magnetic head including a write shield having an end face that is located in the medium facing surface and wraps around the end face of the main pole.
The magnetic head including the write shield is typically provided with one or more return path sections for connecting the write shield and part of the main pole located away from the medium facing surface to each other. The one or more return path sections are configured to form one or more spaces between the main pole and the one or more return path sections. The coil is provided to pass through the one or more spaces. The write shield and the one or more return path sections have the function of capturing a magnetic flux that is produced from the end face of the main pole and spreads in directions other than the direction perpendicular to the plane of the recording medium, and thereby preventing the magnetic flux from reaching the recording medium. The write shield and the one or more return path sections also have the function of allowing a magnetic flux that has been produced from the end face of the main pole and has magnetized the recording medium to flow back to the main pole. Thus, the magnetic head including the write shield allows for preventing unwanted erasure, and also allows for a further improvement in recording density.
U.S. Pat. No. 6,954,340 B2 and U.S. Patent Application Publication No. 2005/0128637 A1 each disclose a magnetic head including, as the aforementioned one or more return path sections, a return path section located on the trailing side relative to the main pole and a return path section located on the leading side relative to the main pole.
Further, JP-A-2009-48719 discloses a magnetic head including a main pole, a first coil of helical shape for energizing the main pole, a leading-side shield located on the leading side relative to the main pole, a trailing-side shield located on the trailing side relative to the main pole, and a second coil for energizing the leading-side shield and the trailing-side shield. In this magnetic head, the main pole is coupled to neither of the leading-side shield and the trailing-side shield. The leading-side shield and the trailing-side shield form respective magnetic paths coupled to each other. The leading-side shield and the trailing-side shield are energized in opposite polarities to each other, whereas the main pole and the leading-side shield are energized in the same polarity.
The position of an end of a record bit to be recorded on a recording medium depends on the position of the trailing-side end of the end face of the main pole located in the medium facing surface. To define the position of the end of the record bit with high accuracy, it is therefore effective to form the end face of the write shield to include an end face portion located on the trailing side relative to the end face of the main pole.
With increases in frequency of write signals for higher recording densities, it is required of the magnetic head to provide an improved rate of change in the direction of the magnetic flux produced from the end face of the main pole. To satisfy this requirement in the magnetic head having the write shield, it is effective to form the end face of the write shield to include an end face portion located on the trailing side relative to the end face of the main pole, as mentioned above. In addition to this, it is effective to provide a return path section that is located on the trailing side relative to the main pole, which will hereinafter be referred to as the trailing-side return path section, and to reduce the length of the trailing-side return path section. To that end, it is effective to reduce the number of turns of the coil passing through the space formed between the main pole and the trailing-side return path section.
Coils used in magnetic heads for perpendicular magnetic recording are broadly classified into two types. A coil of a first type is in the form of being wound about an axis parallel to the direction of travel of the recording medium, and not around the main pole. For example, the coil of the first type can be in the form of being wound around a portion of a return path section. A coil of a second type is in the form of being wound around the main pole.
Each of the coils of the first and second types has advantages and disadvantages as discussed below. The coil of the first type is not wound around the main pole. The coil of the first type thus has a disadvantage that a high proportion of the magnetic flux produced by the coil of the first type tends to fail to pass through the main pole. On the other hand, the coil of the first type has an advantage that it is possible to enhance the magnetomotive force on the return path section to allow the write shield and the return path section to perform the above-described functions effectively.
The coil of the second type is wound around the main pole. The coil of the second type thus has an advantage that most of the magnetic flux produced by the coil of the second type is able to pass through the main pole. On the other, the coil of the second type has a disadvantage that it is not possible to enhance the magnetomotive force on the return path section, so that the write shield and the return path section may become unable to perform their functions effectively.
We now turn to the problem with reducing the number of turns of the coil passing through the space between the main pole and the trailing-side return path section to reduce the length of the trailing-side return path section in order to address the trend toward higher frequencies of write signals. First, where the coil passing through the aforementioned space is of the first type, reducing the number of turns of the coil can result in a reduction of magnetic flux passing through the main pole, and may thus cause the main pole to become unable to produce a write magnetic field of sufficient magnitude. On the other hand, where the coil passing through the aforementioned space is of the second type, reducing the number of turns of the coil may cause the write shield to be degraded in its capability of capturing magnetic flux, and may thus result in the occurrence of unwanted erasure.
Thus, it has conventionally been difficult to produce a write magnetic field of sufficient magnitude from the main pole and make full use of the function of the write shield while reducing the length of the trailing-side return path section.
Note that in the magnetic head disclosed in JP-A-2009-48719, the main pole and the trailing-side shield are not coupled to each other. Thus, this magnetic head has no trailing-side return path section. Accordingly, for this magnetic head, it is impossible to reduce the length of a trailing-side return path section in order to address the trend toward higher frequencies of write signals. Further, in this magnetic head, since the main pole and the leading-side shield are energized in the same polarity, the magnetic flux produced by the leading-side shield may induce unwanted erasure.